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i don't have a pop off valve!


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so with prevention being the best cure for future woes where is the best place to get one?

 

also any hints & tips on fitting would be greatly recieved, i've heard that the 81 onwards engines are a little more difficult? my car has a k&n filter with a carbon airbox cover (that's open on the end), could this be why one wasn't fitted? does the air filter not let the pressure blow through it resulting in the explosion??

 

the airbox itself has all been replaced in the rebuild but i'm struggling to imagine why someone would fit the relatively cheap pop off valve when doing such a rebuild?

 

answers on a postcard please chaps :)

 

(car is an 81 SC by the way)

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so with prevention being the best cure for future woes where is the best place to get one?

 

also any hints & tips on fitting would be greatly recieved, i've heard that the 81 onwards engines are a little more difficult? my car has a k&n filter with a carbon airbox cover (that's open on the end), could this be why one wasn't fitted? does the air filter not let the pressure blow through it resulting in the explosion??

 

the airbox itself has all been replaced in the rebuild but i'm struggling to imagine why someone would fit the relatively cheap pop off valve when doing such a rebuild?

 

answers on a postcard please chaps :)

 

(car is an 81 SC by the way)

IIRC '81 (?) onwards SC's don't need a pop-off valve ? My '82 doesn't have one (but then it doesn't backfire either ;)).

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sounds about right - my '79 SC has one

From a comment on this Pelican article on installing a pop-off valve.

 

These instuctions were perfect except that no one addressed the fact that the air box on the '80 through '83 911SC is modified from the earlier years. In '80 an internal metal manifold was added to the air box. This manifold routed the fuel mist from the cold start valve to the inputs of each air runner to better distribute this mist to each individual cylinder. Prior to this, the cold start valve sprayed fuel into the open intake manifold part of the airbox
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yeah now i've read this thread but to my reading, i'm still not sure that it doesn't need one, as the above comment is in aparagraph warning that fitment of the pop off valve on the 81> models is more difficult as there is something the drill can hit?

I remember/read it as the 'internal metal manifold' in the later model meant the plastic airbox wouldn't explode :twocents:

Edited by GaryH
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ah well thanks for the heads up-i'll double check it with the huge SC book tonight when i get home, if i'm still unsure i'll let you know.

Either way you should take the K&N filter out and just use the stock Porsche one. Unlike other car makes, the 911 SC factory filter is the most efficient one.

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Either way you should take the K&N filter out and just use the stock Porsche one. Unlike other car makes, the 911 SC factory filter is the most efficient one.

 

yep i heard this too gary, thanks for the heads up. i think i'll leave it as is for the time being, the car is plenty fast enough & i'll do that when i get it serviced next year.

 

the first eurohoon is lined up for early april so everything needs fettling in time for that :)

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There is only one air box available now for 3.0 cars, the early one has been superceeded. This later air box is a better design and less likely to explode but still can do. We sell the valves at £30, easy enough to install while the engine is in the car, money well spent when a new box is £240

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There is only one air box available now for 3.0 cars, the early one has been superceeded. This later air box is a better design and less likely to explode but still can do. We sell the valves at £30, easy enough to install while the engine is in the car, money well spent when a new box is £240

 

 

tell you what, i should get 5 mins over the weekend, i'll pop the airbox cover & filter out & take a picture, if you could have a look & tell me what type you think it is i'd be very gratefull, we can take it from there :)

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tell you what, i should get 5 mins over the weekend, i'll pop the airbox cover & filter out & take a picture, if you could have a look & tell me what type you think it is i'd be very gratefull, we can take it from there :)

I've had air boxes go on 1982 year SC's. My current car (SC) now has a pop off valve fitted. Worthwhile IMO.

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I have a pop off valve and have been glad of it a couple of times. Once the whole valve blew out!

 

I can't imagine it would do any harm putting one in, regardless of the year, belt and braces etc.

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Yep, correct Phil, as I said, even the newer boxes will do this at some time, just a question when! When it 1st happened to me I was lucky (no ostriches around) although I was deaf for 30 minutes as I was in a closed garage when it blew, boy it was scary!. I was able to just reglue the 2 halves back and no damage was done but sometimes these can shatter into pieces

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  • 4 weeks later...

I have a 1980 SC Sport and fitted the pop off valve a few years ago when the original air box blew up and had to be replaced at significant cost. The pop off valve is relatively easy to fit and one of the most cost effective modifications you can do on a SC. A few days ago I started the SC for the first time in two months and there was a bang which on inspection had blown the whole relief valve out its hole. After refitting the valve the car started and settled down to a steady tick over. The good news was I could still use the car and secondly there was no damage to the air box. I will, of course, re glue the pop valve back into the hole when I get the chance.

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I have a 1980 SC Sport and fitted the pop off valve a few years ago when the original air box blew up and had to be replaced at significant cost. The pop off valve is relatively easy to fit and one of the most cost effective modifications you can do on a SC. A few days ago I started the SC for the first time in two months and there was a bang which on inspection had blown the whole relief valve out its hole. After refitting the valve the car started and settled down to a steady tick over. The good news was I could still use the car and secondly there was no damage to the air box. I will, of course, re glue the pop valve back into the hole when I get the chance.

 

 

Sorry guys.

 

How do you know if you have one or not?

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the last sc I saw blow up from not having a pop off valve fitted the owner was ejected from his seat and ended up in a field full of gay ostriches

The aftermath wasnt pretty

 

was that a targa or a coupe with a sunroof?

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My 81 SC air box went bang about 8 years ago my ears are still ringing now, my wallet also still hurts a new air box is'nt cheap, i fitted a pop off valve after that.

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Dom, the pressure builds from underneath the pop off valve in the plenum below where the fuel and air mixture is drawn into the inlet manifolds. The cold start valve injects direct to that area and any odd spark can ignite it. Porsche tried to resolve the problem with the later airboxes by fitting metal pipework inside the plenum to direct the cold start flow directly to each inlet manifold but they still can blow.

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